When the battery level drops below ~20% on a MacBook Pro or MacBook Air, macOS will decrease 10/25G Ethernet transmit performance in order to conserve battery life for the laptop.
The original Solo10G was built with the Marvel AQ107s, which Apple started supporting with macOS 10.13 (High Sierra)+.
When Marvel discontinued the AQ107s, Sonnet adopted a newer part. Solo10Gs starting with C01248 084 029905 have an AQ113cs. Apple supports the AQ113cs with macOS 12 (Monterey)+.